1. Field of the Invention
The present invention relates to a motor with improved heat dissipation effect, and more particularly, to heat dissipation means for linear motor.
2. Description of the Prior Art
A stator and a rotor are two essential components of a motor. In general, the stator has armature windings for carrying load current, and the rotor is provided with a magnetic field formed of field windings on an iron core of laminated sheet steel. After the field windings are ready, the insulating material for example, epoxy resin, or other equivalents are enclosed over the windings and the core. With this structure, the motor converts electric energy to rotating torque according to the Fleming""s left hand rule.
The energy of a motor is partially converted into heat which in turn gives rises to increase of winding resistance and I2R loss of the motor. As a result, the temperature rise of the motor is exacerbated to greatly lower the motor efficiency. It is well understood that both the stator and rotor is hard to cool down especially in the case the windings and the core are enclosed with thermal insulating epoxy resin.
The motor may be classified into rotating type and linear type. In the rotating type, the motor can be equipped with ventilation means such as cooling fans or providing ventilation holes through the laminated core so as to take away heat generated during operation of the motor. Unfortunately, such means are not applicable to a linear motor so that certain other heat dissipation mechanism must be added to it.
FIG. 6 shows conventional means for heat dissipation in a linear motor. In this case, the mover 25 of the linear motor includes an iron core 19 with field windings 20 wound on the iron core 19, and a heat dissipation plate 18 attached on top of the core 19, or attached to the front or the rear end, or to both sides. By heat exchange function performed by a refrigerant flowing in the cooling pipes contained in the heat dissipation plate 18, heat is carried out of the motor. However, in this case, only the heat existing on the uppermost part or on both sides of the mover 25 can be dissipated, dissipation of heat loitering at the center portion of the core 19 and in the field windings is not easy and the heat dissipation efficiency for the entire motor is quite poor.
Another improvement made by U.S. Pat. No. 4,839,545 to upgrade the heat dissipation effect is shown in FIG. 7. As shown in FIG. 7, a plurality of silicon sheet steels 21 for the mover 26 are formed into various configurations so as to facilitate burying refrigerant contained cooling pipes into a meandering groove 22 on the sheet steels 21. Meanwhile, several sets of expensive dies have to be prepared for complicated fabricating process. Besides, the mover 26 becomes bulky for the resin containing cooling pipes therein. Moreover, refrigerants are generally corrosive so that the motor windings are apt to be damaged in case of leakage of refrigerant.
Another well-known heat dissipation means for a linear motor was provided by U.S. Pat. No. 5,751,077. In this disclosure, the principles of cooling an oil immersed transformer is employed wherein by filling a none electric and magnetic conducting liquid into a housing of the mover. Meanwhile, for perfectly carrying out the advantage of this design, a perfectly leak proof mover housing must be provided at first, which is not only difficult in manufacturing, but also expensive for production cost. Besides, weight of the mover will be inevitably increased, and an additional device for circulation of the cooling liquid in the mover with other external equipment for heat exchange. One thing more, the fear of damaging electrical circuit of the motor in case of leakage of refrigerant still remains unsolved!
Another solution for heat dissipation of a linear motor is shown in FIG. 8. A linear motor 27 is composed of a stator 28 and a mover 29, pressurized air 23 is blown onto the surface of the mover 29. Incidentally, in this method, the heat hidden in the inner part of the mover 29 enclosed by an epoxy resin layer or other equivalents 24 is hard to expel. Besides, additional cost for preparing an air compressor together with an air reservoir is considerably expensive.
The present invention has been made in order to eliminate the inconvenience and disadvantages inherent to the conventional techniques as mentioned above. The essential object of the present invention is to provide heat dissipation means for a linear motor, with such means, the heat produced by the motor can be effectively carried away therefrom so as to perform heat dissipation with a high efficiency heat exchange procedure.
In the present invention, thermal conducting pipes and a heat dissipation gel instead of conventional cooling circulation pipes buried in the iron or windings. With this structure, the small sized light weighted, and non-ferrite heat conducting pipes are able to be buried deeply into the core or windings of the motor beneath the epoxy resin so as to perform highly efficient heat dissipation.
In the present invention a thermal conducting pipe is used, comprising a closed, vacuum-tight envelope, a porous lining called a xe2x80x9cwick structurexe2x80x9d, and a moving fluid. The thermal conducing pipe, also known as a heat pipe, is an efficient heat transfer device recently used in the electronics industry, especially in laptop computers. The thermal conducting metallic tubes are almost completely evacuated, filled with a small amount of special liquid materials, for example, methane or acetone having a low boiling point, and a material with capillary characteristics. As the pipes are heated, pressure variation in the pipes causes evaporation of the liquid with the result that vaporized liquid flows with a very high velocity from a high temperature region to a low temperature region. As soon as the vaporized liquid comes in contact with the wall surface of the metallic pipes at the low temperature region, heat is conducted to the wall surface of the low temperature metallic pipes. After having released the heat energy, vaporized liquid restores its liquid state and flows back to the high temperature region with the aid of gravity or by capillary action of the capillary material. By such repeated circulation, the heat produced by copper loss and iron loss during operation of the motor is carried away from the iron core and the windings directly outside through the metallic pipes without detention by the epoxy resin layer.
In the present invention, for further enhancing heat dissipation effect, a metallic heat dissipation plate is attached to the outer surface of the mover, the heat dissipation plate is in contact with the metallic pipes so as to assist the heat dissipation thereof. During operation, the heat is dissipated to the air from the heat dissipation plate without providing any additional means for forced cooling. Fins can be provided for the heat dissipation plate to increase contact area with air thereby improving heat dissipation effect.
In the present invention, a recirculating circuit for refrigerant can be formed in the heat dissipation plate which is in contact with the thermal conducting metallic pipes for assisting to dissipate heat to the air in the case of a large motor producing great amount of heat. However, the metallic heat dissipation plate is located far away from the core and windings so that there is no fear of leakage of refrigerant which might cause a short circuit of the motor.
In the present invention, a thermal conducting gel can be filled between the metallic thermal conducting pipes and the heat dissipation plate thereof for further improving the thermal conducting effect.
Besides, the technique of the present invention is all applicable to a rotating motor.